Art of preparing nitrocelluloses and raw material therefor



Patented Dec. 1,: 1931 UNITED STATES PATENT: OFFICE MILTON O. SCHUR AND BENJAMIN G. HOOS, OF BERLIN, NEW HAMPSHIRE, ASSIGNORS TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE ART OF PREPARING NITROCELLULOSES AND RAW MATERIAL THEREFOR No Drawing. I

This invention relates to the art of nitrating cellulose fiber to produce a product intended for use in the manufacture of films, lacquers, artificial silk, and the like, its object being to make possible a high yield of 'good quality product having a low acid re- 'tention.

In application Serial No. 140,674, filed October 9, 1926, by George A. Richter, Milton O. Schur, and Royal H. Rasch, and issued October 1, 1929, as Patent No. 1,7 29,628, various methods of conditioning cellulose fiber to render it more suitable as a raw material for nitration are disclosed. All those methods involve a treatment which renders the fiber less absorptive and reactive, as it has been found that the nitrating reaction is thereby modified in such a way as to result in a high yield of product having a low acid retention. The theory advanced in that case is that the sulphuric acid in the nitrating bath tends to gelatinize and to hydrolyze the cellulose fibers, especially if the pulp is highly absorptive. If, however, as explained in that application, the fiber is beaten, treated with regenerated cellulose or with nitrocel lulose, or is otherwise rendered less reactive, side reactions are apparently retarded or avoided and nitration proceeds smoothly. A thin coating or film of dry nitrocellulose on the fibers, for example, probably allows nitric acid to penetrate into the fiber wall more easily than it does the sulphuric acid and perhaps readily allows water generated within the fiber during nitration to diffuse into the main body of the nitrating acid, so that within the fiber wall there is believed to be a nitric-acid-rich mixture which has a greatly reduced gelatinizing tendency and which nitrates the cellulose before hydrolysis proceeds toa-ny troublesome degree. It is well known for example, that nitrating acids rich in nitfic acid give high yields, but that acids rich in sulphuric acid cause hydrolysis and correspondingly low yields. The thin coating or film applied to the fibers prior to nitration, by 'slowingup the reaction, eliminates local over-heating in the acid bath, and may also thus prevent loss in yield, for the higher the temperature of nitratlon, the

presence in more than traces'is objectionable,

Application filed January 31, 1923. Serial No. 336,633.

greater is the tendency for the yield to drop because of side reactions. Another function of the protective coating or film may be to cement the loosely adhering surface fibers to the body of the sheet or shreds of pulp, thereby counteracting the tendency of the nitrated surface fibers to pass into colloidal solution in the nitrating acid and to become lost 'durin-gthe separation of the spent acid from the nitrocellulose in the centrifuge.

In accordance with the process of the present invention, we treat fiber with acid-repellent material such .as waxes and oils, as we have discovered that the use of a very small amount of such material results in marked improvements upon subsequent nitration of the fiber. Apparently, such materials, even when they produce an exceedingly thin coating or film on the fibers, sufficiently protect the cellulose from gelatinization and hydrolysis during nitration to bring about'the desired results. Preferably, the acid-repellent material employed is free from objectionable color-yielding or stability-lowering matter,paraflin oil, parafiin wax, and stearic acid being examples of material of this type. l/Ve believe that waxy or resinous material such as naturally occurs in the fiber exerts a protective influence during nitration, but its 80 because it tends to make the fiber float on the nitrating acid, with the attendant risk of pot fires and non-uniform nitration, because such material is usually associated with color-yielding compounds, and I because its composition is variable and uncertain. The process of the present invention may therefore be applied to especial advantage in the case of wood pulp, particularly those pulps which have been refined to high alpha sellulosecontentbytheremoval of beta and'gamma celluloses, lignin, and resins.- Such purified wood pulp, by reason of its lower cost, may be used to advantage as a substitute for highly refined cotton fiber in the preparationof 95 nitrocelluloses, but it has been found that it may under some conditions give a slightly lower yieldof product than the cotton fiber.

1 By the process of the present invention, howmay be improved at low expense to render it a more perfect raw material for nitration.

The acid-repellent material may be applied to the fiber in various ways, using liquid carrying agents, as by dispersing such material in water or dissolving in organic solvents. The carrying agent may then be removed from the fiber before. nitration, as by drying, so as to avoid dilution of the nitrating acids. For instance, parafiin oil, Wax, stearic acid,or like material, may be dispersed in a small amount of water containing small quantities of a soap, such as potassium oleate, as the dispersing agent. Or main the beater engine, and the oil or wax fixed on the fibers through the use of, say, alum, or other precipitating agent, in much the same way that rosin size is precipitated on pulp in the beater engine.

traces of the protective agent are needed in the fiber, the alum or other fixing agent may be omitted. The fiber ma then be sheeted on a paper machine, and t e paper nitrated.

, Or pulp may first be sheeted; into paper and the sheet of paper may then be passed through a dispersion or solution of the acidrepellent material, whereupon the liquid carrier may be removed by vaporization, and the paper nitrated.

Experiment has shown that through the incorporation of as low as 0.1% parafiin wax, stearic acid, or the like, in the form of a dispersion, to comparatively free pulp, followed by the fixing of the parafiin on the fibers, the

' sheeting of the pulp into paper, and the nitration of the paper, we may realize yields of nitrocellulose which compare favorably with those attained when the fiber is well beaten. It is thus possible to avoid the more expensive expedient of thoroughly'beating the fiber prior to sheeting into paper, in order to in crease yield and at the same time produce a raw material from the comparatively free fiber as suitable as that obtained from thor.

oughly beaten fiber.

In order to appreciate the. utility of the process of our invention, a specific example of procedure will now be given, according to whlch a sheet of paper made of a refined wood pulp was treated with a paraifin wax dispersion in water, dried, and then nitrated.

The wood pulp employed as a raw material was a sulphite pulp which had been refined Or, since only ticity of films by cooking in a caustic soda solution containing oleic acid, which served to remove beta and gamma celluloses and resinous impurities from the pulp. The pulp was then bleached and the bleached pulp sheeted into perslon of acid-repellent material was prepared by vigorously agitating a solution of parafiin wax in kerosene with a dilute solution of soap in Water, whereupon the mixture paper of 30 pounds basic weight. A dis- 4 was passed through a colloid mill to ensure thorough dispersion. The resulting dispersion was diluted with water until the ratio of paraflin to water was 1 tq12,000. This dilute dispersion served as a bath through which the dry sheet of paper was passed. The paper thus treated, when dried, showed no signs of wax, either in appearance or feel. When nitrated at 40 0., it gave a theoretically perfect yield of nitrocellulose which when dissolved in suitable solvents gave solutions of marked clarity and sparkle. Following are tabulated results obtained from treated and untreated papers when nitrating acid containing 20.5% HNO 60.8% H SO and Untreated Treated paper paper Per cent wax added to sheet 0 0.025 Yield on nitratiom. 150. 7 154. 8 Initial temperature rise of nitrating bath- 1. 4 1.2 Viscosity of nitrocellulose 6. 7 8. 3 Per cent nitrogen in nitrocellulose 11. 00 11. 00 Per cent theoretical yield realized 97. 4 100.0

, Bursting strength of film 104 110 Tensile strength of film 4530 5370 Tensile stretch of film 13. 5% 20. 0%

" 18.7% H O was used at 40 C. for 30 minutes (The ratio of weight of acid to. fiber was 50 to 1, and the paper was shredded into small pieces before nitration.)

It is noteworthy to remark that the shredded paper containing wax had little or no tendency to stick to the sides of the nitrating pot, whereas the run in which untreated paper was employed had to be closely watched, shreds being scraped from the sides ofthe pot in order to ensure complete nitration. It

is noteworthy that while a slight amount of acid-repellent material such as paraffin wax effects the beneficial improvements indicated 1n the foregoing table, more than, say, 0.2% is apparently unnecessary and may be detrimental, in that nitration may be retarded to too great an extent and hence necessitate an excess vely long time of reaction for complete nltration, and the fiber may tend to float on the acid. But with under, say, 071% adde d wax, although the reaction is slowed down materially, complete reaction is realized in a reasonable time and no serious tendency of the fiber to float is manifested. As further indicatedin the table, the presence of wax ,in

the paper improved the strength and elasnitrocellulose.

Another example of procedure according prepared from the resulting to which dispersed parafiin wax was incorporated into pulp and fixed on the fibers before sheeting into paper and nitrating was substantially as follows. One thousand pounds of refined wood pulp of the type here- ,inbefore described was placed in a beater engine and water disseminated therethrough to produce a stock density of about 5% (bonedry basis). To the stock was then added 125 gallons of a dispersion of paraffin wax prepared by dissolving 4% pounds of wax in 9 pounds of warm kerosene, shaking vigorously with 50 pounds of warm water containing 1.9 pounds of potassium oleate dissolved therein, and diluting the resulting dispersion to 125 gallons. he beater charge was brought to a slowness corresponding to slightly less than that of stock intended for bond paper, and

was run directly over the paper machine.

The paper was found to contain about ).1%

of added wax. Upon nitrating such paper as previously described, a yield of 156.7 and a nitrogen content of 11.20 were obtained, corresponding to a theoretical yield of 99.9%.

Having thus described certain embodiments of this invention, it should be evident to those skilled in the art that various changes and modifications might be made therein Without departing from the spirit or scope of invention as defined by the appended claims.

We claim:

1. A process which comprises treating cellulose fiber with non-cellulosic, acid-repellent material and then nitrating the fiber.

' 2. A process which comprises treating cellulose fiber with parafiin Wax and then nitrating the fiber.

3. A process which comprises treating cellulose fiber with non-cellulosic. acid-repellent material and a liquid carrier for said material, and then nitrating the fiber.

4. A process which comprises treating cellulose fiber with non-cellulosic, acid-repellent material and a liquid carrier for said material, removing thecarrier, and then nitrating the fiber.

5. A process which comprises treating cellulose fiber with an aqueous dispersion of acid-repellent material, and then nitrating the fiber.

6. A process which comprises treating cellulose fiber with an aqueous dispersion of acid-repellent material, drying, and then nitrating the fiber.

7 A process which comprises treating cellulose fiber with an aqueous dispersion of piraifin wax, drying, and then nitrating the fi er. i

8. A process which comprises treating cellulose pul with an aqueous dispersion of acid-repel ent material, sheeting into paper, and nitrating the paper.

9. A process which comprises treating cellulose pulp with an aqueous dispersion of acid-repellent material, fixing such material on the fibers, sheeting into paper, and nitrating the paper.

10. A process which comprises treating cellulose pulp with an aqueous dispersion of paraflin wax containing soap as a dispersing agent, sheeting into paper, and nitrating the paper.

11. A process which comprises treating cellulose pulp with an aqueous dispersion of paraffin wax containing soap as a dispersing agent, precipitating the wax on the fibers, sheeting into paper, and nitrating the paper.

12. A process which comprises treating paper with non-cellulosic, acid-repellent material, and then nitrating the paper.

13. A process which comprises treating pa per with parafiin wax, and then nitrating the paper.

14. A process which comprises treating paper with a. liquid. carrying non-cellulosic, acid-repellent material, removing the liquid from the paper, and nitrating the paper.

15. A process which comprises treating paper with an aqueous dispersion of acid-re pellent material, and nitrating the paper.

16. A process which comprises treating pa signatures.

MILTON O. SCHUR. BENJAMIN G. HOOS. 

